Pathogenicity Studies with the Fungi Aphanomyces invadans, Achlya bisexualis, and Phialemonium dimorphosporum: Induction of Skin Ulcers in Striped Mullet

Abstract

Based on isolations from naturally infected fish in Florida, we investigated the role of the fungi Aphanomyces invadans, Achlya bisexualis, and Phialemonium dimorphosporum in the etiology of ulcerative mycosis (UM) in striped mullet Mugil cephalus. We injected healthy striped mullet subcutaneously with secondary zoospores of four oomycete isolates: two concentrations (50 and 115 zoospores/mL) of SJR (an endemic isolate of Aphanomyces invadans in American shad Alosa sapidissima from the St. Johns River); two concentrations each of CAL (25 and 65 zoospores/mL) and ACH (1,400 and 2,000 zoospores/mL; endemic isolates of Aphanomyces invadans and Achlyva bisexualis, respectively, in striped mullet from the Caloosahatchee River); and two concentrations of the ascomycete culture MTZ (2,500 and 3,500 zoospores/mL; endemic isolate of P. dimorphosporum from whirligig mullet M. gyrans in the Matanzas Inlet). All fish injected with either concentration of SJR developed granulomatous ulcers after 8 d and died within 21 d. Eighty percent (8/10) of fish injected with the high dose of CAL developed ulcers after 13 d and died within 28 d, but only 30% (3/10) of fish injected with the low dose of CAL developed ulcers. Four of the ulcerated fish died within 28 d, and the remaining fish were terminated after 32 d. Fish injected with zoospores of Aphanomyces invadans developed ulcers that were grossly and histologically similar to those observed in naturally infected striped mullet with UM from several estuaries or rivers in Florida. These hemorrhagic skin ulcers were characterized by myonecrosis and the presence of mycotic granulomas. None of the fish injected with ACH, MTZ, or sterile water developed ulcers. This study fulfilled Koch's postulates and demonstrated that ulcers could be experimentally induced in striped mullet after exposure via injection to secondary zoospores of an endemic Florida strain of Aphanomyces invadans.

Deciphering microbial landscapes of fish eggs to mitigate emerging diseases

“…Achlya species have been described for diseased fish in natural environments (Jeney and Jeney, 1995;Kales et al, 2007;Sosa et al, 2007), and A. invadans is a notorious pathogen of different natural and farmed fish species worldwide, except in Europe and South America (Oidtmann, 2012). Both Achlya and Aphanomyces spp.…”

Vitamin C and endogenous cortisol in foreign-body inflammatory response in pacus

“…Multinucleated giant cells (MGC) have been described in fish with bacteriosis (Olsen et al, 2006;Swaim et al, 2006;Jacobs et al, 2009), parasitosis (Adriano et al, 2005Hogge et al, 2008), and fungus (Sosa et al, 2007;Oidtmann et al, 2008), with in Pesq. agropec.…”

Diseases and Mortalities of Fishes and Other Animals in The Gulf of Mexico

“…The related fungus Aphanomyces invadans occurs as an ulcerative skin lesion in the Atlantic menhaden (Brevoortia tyrannus) (Figure 14.7) along the Atlantic coast; the lesion and associated mortalities had been previously attributed to the dinoflagellate Pfiesteria piscida until the critical investigations by Blazer et al (1999) and Vogelbein et al (2001). Similar ulcerative lesions have been reported from the striped mullet, silver mullet, black drum, sheepshead, and silver perch in the Gulf from Florida, so Sosa et al (2007) conducted an experimental study with Aphanomyces invadans and other oomycete fungi in the striped mullet and determined that only it caused the lesion. Other fungi such as Lacazia loboi causes infections (lobomycosis) in offshore bottlenose dolphin extending into the Gulf (Rotstein et al 2009).…”